In order to avoid the bottleneck (limits of bandwidth, signal amount) of the electrical wiring techniques in signal switching in a high speed router, applying an optical packet switch utilizing the high bandwidth characteristics of optical transmission techniques has been studied, and the optical packet switch has been partially introduced. The optical packet switch system which has been introduced so far, once converts an optical signal to an electrical signal to perform switching. Thus, as the bandwidth has been increased, a scale of switch has been expanded. In order to avoid a drastic expansion of the scale of switch, an optical packet switching apparatus which switches an optical packet inputted thereto and sends out the optical packet as it is without converting the optical packet inputted to an electrical signal has been thought.
FIG. 1 illustrates an example of an optical packet switching apparatus that is conventionally thought.
The optical packet switching apparatus illustrated in FIG. 1 is a simplified optical packet switching apparatus for the easiness of illustration and description, and includes an input system of two channels and an output system of two channels.
The optical packet switching apparatus 10 illustrated in FIG. 1 includes an optical packet transmission section (OPTS) 20, an optical switch section (OSS) 30, an optical monitor section (OMS) 40, a control section (CTLS) 50 and a center section (CS) 60.
The optical packet transmission section (OPTS) 20 includes two channels of optical transmission lines 211, 212 on the input side from which optical packets 701, 702 are inputted respectively. The optical packets 701, 702 inputted from the respective optical transmission lines 211, 212 are separated to headers 701a, 702a which include destinations and data information(payloads 701b and 702b) which is main bodies of the optical packets 701, 702. The headers 701a, 702a and the payloads 702b, 702b of the optical packets 701, 702 are different in the optical wavelength from each other. Optical filters (OF) 221, 222 separate the optical packets 701, 702 into the headers 701a, 702a and the payloads 701b, 702b, by using a difference of the wavelength.
The headers 701a, 702a of the optical packets 701, 702 are converted into electrical signals by photo detectors (PD) 511, 512 for the respective channels provided in the control section (CTLS) 50 to be inputted to an enable signal generation section (ESGS) 513.
In the enable signal generation section (ESGS) 513, according to destination information written in the headers 701a, 702a, an enable signal for switching plural optical switches (described later) included in an optical switching circuit (OSC) 30 provided in the optical switch section (OSS) 30 is generated to be inputted through six of signal transmission lines 514-1, 514-2, 514-3, 514-4, 514-5, 514-6 to the optical switching circuit.
In contrast, the payloads 701b, 702b separated by the optical filter (OF) 221, 222 are inputted to the optical switch circuit (OSC) 31 of the optical switch section (OSS) 30.
FIG. 2 is a block diagram illustrating a configuration of an optical switching circuit illustrated as one block in FIG. 1.
The optical switching circuit (OSC) 31 includes two of input ports 311, 312, two of photo couplers 321, 322, two of optical switch modules 331, 332 and two of output ports 341, 342. In addition, the two of optical switch modules 331, 332 each includes two upstream side optical switches 331_1, 331_2 and 332_1, 332_2, one photo couple 331_1 and 332_3, and one downstream side optical switches 331_4 and 332_4, respectively.
When an optical packet is inputted from the input port 311 of a first channel, the optical packet is divided into two pieces by the photo coupler 321 to be inputted to the optical switch 331-1 of the first channel and the optical switch (OSW) 332_1 of a second channel on the upstream side. And, similar to this, when an optical packet is inputted from the input port 312 of a second channel, the optical packet is divided into two pieces by the photo coupler 322 to be inputted to the optical switch 331-2 of the first channel and the optical switch 332_2 of the second channel on the upstream side. The optical packets each inputted to the two optical switches 331_1, 331_2 of the first channel respectively are, via each of the optical switches 331_1, 331_2 when the optical switches 331_1, 331_2 are in the on state, further via the photo coupler 331_3, and furthermore via the optical switch 331_4 when the optical switch 331_4 on the downstream side is on, outputted from the output port 341 of the first channel.
In addition, similar to this, the optical packets each inputted to the two optical switches (OSW) 332_1, 332_2 of the second channel respectively are, via each of the optical switches 332_1, 332_2 when the optical switches 332_1, 332_2 are in the on state, further via the photo coupler 332_2, and furthermore via the optical switch 332_4 when the optical switch 332_4 on the downstream side is in the on state, outputted from the output port 342 of the second channel.
Thus, when the first optical switch (OSW) 331_1 on the input side of the first channel and the optical switch (OSW) 331_4 on the output side of the first channel are in the on state, and the second optical switch (OSW) 331_2 of the first channel is in the off state, the optical packet inputted from the input port 311 of the first channel is outputted from the output port 341 of the first channel. When the second optical switch 331_2 on the input side of the first channel and the optical switch (OSW) 331_4 on the output side of the first channel are in the on state, and the first optical switch 331_1 of the first channel is in the off state, the optical packet inputted from the input port 312 of the second channel is outputted from the output port 341 of the first channel.
In addition, regarding the second channel, similar to the first channel, when the first optical switch (OSW) 332_1 on the input side of the second channel and the optical switch (OSW) 332_4 on the output side of the second channel are on the on state, and the second optical switch (OSW) 332_2 on the input side of the second channel are in the on state, the packet inputted from the input port 311 of the first channel is outputted from the output port 342 of the second channel. When the second optical switch (OSW) 332_2 and the first optical switch 332_1 on the input side of the second channel is in the off state, the optical packet inputted form the input port 312 of the second channel is outputted form the output port 342 of the second channel.
As described above, the optical switching circuit (OSC) 31 includes two of the input ports 311, 312 and two of the output ports 341, 342, and may output the optical packet inputted from either one of the two of the input ports 311, 312, from either one of the two of the output ports 341, 342.
In addition, the optical switches (OSW) 331_1, 331_2, 331_4, 332_1, 332_2, 332_4 are connected to six of signal transmission lines 514_1, 514_2, 514_3, 514_4, 514_5, 514_6 which extend from the enable signal generation section (ESGS) 513 illustrated in FIG. 1, respectively. On-off of the respective optical switches (OSW) 331_1, 331_2, 331_4, 332_1, 332_2, 332_4 is controlled, by the respective enable signals transmitted through the signal transmission lines 514_1, 514_2, 514_3, 514_4, 514_5, 514_6.
Note that in order to simplify the description, the example in which the output ports are provided two each has been described, however, a case where an optical switching circuit having more input ports or output ports is similar to the example.
Returning to FIG. 1, the description about the optical packet switching circuit 10 of FIG. 1 will be continued.
The optical packets outputted from each of the output ports 341, 342 of the optical switching circuit (OSC) 31 are transmitted through two optical transmission lines 351, 352 on the output side, respectively.
Note that although the optical transmission lines 351, 352 on the output side in FIG. 1 (and in other figures described later) are illustrated as outputting only the payloads 701b, 702b of the optical packets 701, 702, actually, new headers are added to the respective payloads 701b, 702b to be outputted by a configuration not illustrated here.
The optical monitor section (OMS) 40 is provided with two input side photo detectors (IPD) 411, 412, where respective light quantities of the optical packets (payloads 701b, 702b) for the two channels inputted to the optical switch section (OSS) 30 are detected. Light quantity monitor signals detected by the two input side photo detectors (IPD) 411, 412 are converted to input monitor values as digital signals by the A/D converter 42, and are inputted to an input level monitor circuit (ILMC) 515 included in the control section (CTLS) 50.
Similar to this, the optical monitor section (OMS) 40 is provided with two output side photo detectors (OPD) 431, 432, where light quantities of the optical packets (payloads 701b, 702b) for the two channels outputted from the optical switch section (OSS) 30 are detected. Light quantity monitor signals detected by the two output side photo detectors (OPD) 431, 432 are converted to output monitor values as digital signals by the A/D converter 44, and are inputted to an output level monitor circuit (OLMC) 516 included in the control section (CTLS) 50.
Input level specification values (upper limit value and lower limit value) of the input side optical packet and output level specification values (upper limit value and lower limit value) of the output side optical packet are stored in a register section (RGS) 517 provided in the control section (CTLS) 50. The input level specification values are inputted to the input level monitor circuit (ILMC) 515 and the output level specification values are inputted to the output level monitor circuit (OLMC) 516.
In the input level monitor circuit (ILMC) 515, the input monitor value of the input side optical packet inputted from the A/D converter 42 is compared with the input level monitor value received from the register section (RGS) 517 and a comparison result is transmitted to the center section (CS) 60.
Similar to this, in the output level monitor circuit (OLMC) 516, the output monitor value of the output side optical packet inputted from the A/D converter 44 is compared with the output level specification value received from the register section (RGS) 517, and a comparison result is transmitted to the center section 60.
The center section (CS) 60 includes an alarm calculation block which collects monitor results in each section to be recorded and outputs an alarm.
Note that although the center section 60 is illustrated here as being provided in a single optical packet switching apparatus 10, single of the center section may be provided for whole plural optical packet switching apparatuses and my be integrally play a role to collect the monitor result and to output the alarm in the plural optical packet switching apparatuses.
When the optical packet switching apparatus 10 as illustrated in FIG. 1 is thought, although it is determined that whether or not the optical quantities of the optical packet on the input side and the optical packet on the output side are satisfied with the references is monitored in the input level monitor circuit (ILMC) 515 and the output level monitor circuit (OLMC) 516, for the configuration illustrated in FIG. 1 as it is, it is not known whether it is a timing when the optical packet is currently inputted, and it is not known in what on-off state the optical switches included in the optical switching circuit (OSC) 31 are and through what path the current detected optical packet has passed, and there is a problem that it is difficult to determine whether or not an abnormality occurs. In addition, even though it is determined that an abnormality has occurred, there is a problem that it is difficult to specify whether or not the abnormality is in an optical path or the abnormality is in the detection system for detecting whether or not there is an abnormality.
Here, in Japanese Patent Application Laid-open, No. H11-122220, there is disclosed a technique to detect an abnormality of an output level of an optical signal at plural places while the application field is different. However, the technique disclosed in Japanese Patent Application Laid-open, No. H11-122220 also has a problem similar to that explained referring to FIG. 1, considering that the application filed of the technique is changed to be applied to an optical packet switching apparatus.
In addition, in Japanese Patent Application Laid-open No. H11-8590, there is proposed a technique to control states of plural apparatuses included in an optical transmission system.
Further, in Japanese Patent Application Laid-open No. 2005-269668, there is proposed a technique to stabilize a phase of a control signal of an optical switch that demultiplexes an optical multiplexed signal.
However, the detection ways described in Japanese Patent Application Laid-open No. H11-8590 and Japanese Patent Application Laid-open No. 2005-269668 may not be applied to an optical packet switching apparatus.
In view of the foregoing, it is an object of the present invention to provide an optical packet switching apparatus including means of monitoring that readily detects an abnormality.